Method for electrodepositing manganese

ABSTRACT

AN IMPROVED METHOD OF ELECTRODEPOSITION MANGANESE METAL USING AS A CATHODE AN ALLOY OF STAINLESS STEEL AND SELENIUM.

United States Patent O 3,686,083 METHOD FOR ELECTRODEPOSITING MANGANESE San-Cheng Lai, Oklahoma City, Okla., assiguor to Kerr- McGee Chemical Crp., Oklahoma City, Okla. No Drawing. Filed Nov. 25, 1970, Ser. No. 92,919 Int. Cl. 301k 3/06; C22d 1/00 US. Cl. 204-105 M Claims ABSTRACT OF THE DISCLOSURE An improved method of electrodepositing manganese metal using as a cathode an alloy of stainless steel and selenium.

BACKGROUND OF THE INVENTION It is well known in the field of electrodeposition of manganese metal to use electrolyte cells including cathodes of stainless steel and an electrolyte containing sulfur dioxide as an additive. However, in commercial practice when using such a cell, it has been found that current efficiencies in the cell are only about 60 to 65%.

In an article Effect of Selenious Acid on the Electrodeposition of Manganese, by A. I. Rao, Y. D. P. Rao, and R. Vedaraman, published in the Nov.-Dec. 1966 (volume 4) issue of the Journal of Electrochemical Technology, it was reported that when selenious acid was used as an additive in place of sulfur dioxide in the electrodeposition of manganese metal, current efliciencies in excess of 90% could be obtained. Further, it has been reported that higher current densities can be used when selenium is used as the additive and that its use resulted in lower cell voltages compared with conventional sulfate bath electrolytes wherein sulfur dioxide is used as the addition agent. However, the use of selenium does have a disadvantage in that the manganese metal deposited is contarninated with selenium.

More recently, it was discovered that when a selenium compound was used as the additive, a precipitate of amorphous selenium formed in the electrolyte. This is disadvantageous, of course, because the selenium is thereby removed from the electrolyte solution and the advantages of its presence are lost, thus necessitating a constant replenishment of selenium to the electrolyte. Further, costs are increased because of the necessity of having to replace the selenium which is precipitated out of the solution.

SUMMARY OF THE INVENTION It has now been discovered that if the cell is modified to include a cathode comprising an alloy of stainless steel and selenium, the manganese metal electrodeposited is substantially free of selenium contamination. Further, selenium losses in the electrolytes are substantially eliminated while the advantages of operating at higher current efficiencies are retained. Thus the use, as a cathode, of an alloy of stainless steel and selenium retains the benefits gained from adding selenious acid to an electrolyte while virtually eliminating or substantially minimizing the problems of selenum losses through precipitation as well as selenium contamination of the deposited manganese. Moreover, it is no longer necessary to constantly replenish the supply of selenium to the electrolyte.

Patented Aug. 22, 1972 The term stainless steel as used herein means those steels commonly referred to as 200, 300 and 400 types of stainless steel. The preferred steels are the austenitic and martensitic stainless steels. However, as those skilled in the art will appreciate, any steel which can be alloyed with selenium would provide a cathode suitable for use in accordance with this invention. The stainless steels are preferred as they are more corrosion resistant.

The selenium content of the stainless steel may be from about 0.1 percent to 0.7 percent, by weight, based on the total weight of the finished alloy. However, particularly good results have been obtained when the selenium content of the stainless steel was in the range of from about 0.15 percent to 0.3 percent, by weight.

While it will be apparent to those skilled in the art that there are a number of stainless steel-selenium alloys that would be satisfactory for the cathode of the instant invention, the commercial availability of 303 Se; 347 FSe; 416 Se: 420 FSe; 430 FSe and 440 FSe alloys makes those the preferred alloys.

The stainless steel-selenium alloy cathode of the present invention may be used in any of the electrolytes commonly used for the electrodeposition of manganese metal such as for example: ammonium chloride and manganese chloride electrolytes or ammonium formate and manganese formate electrolytes.

The preferred electrolyte is an aqueous mixture of ammonium sulfate, sulfur dioxide and a source of manganese ions. The ammonium sulfate is generally present in an amount of from about to 150 gm./liter. The manganese ions, usually introduced into the electrolyte in the form of manganous sulfate, are generally present in an amount of from about 14 to 35 grn./l. Particularly good results have been obtained when the electrolyte contained an aqueous solution of from about to gm./1iter of ammonium sulfate, from about 24 to 35 grin/liter of Mn++ and from about 0.15 to 0.2 gm./liter of 50 When using the preferred ammonium sulfate electrolyte just described, the preferred operating conditions are at a temperature maintained within the range of about 32 to 40 C., a pH within the range of from about 7.5 to 8.0 and a current density of from about 35 to 45 a.s.f.

The following specific examples are set forth to further illustrate, not to limit, the invention.

EXAMPLE I An electrolyte was prepared containing the following ingredients and operated under the indicated electrolysis conditions in the tests to be described.

Ammonium sulfate-430 gm./l. Mn++--25 gm./l. Temperature-35 C.

Three tests were run. In Test No. l, a conventional stainless steel was used as the cathode. In Test No. 2, selenious acid was employed as an additive in the electrolyte. In Test No. 3, the improved results obtained using, as the cathode, a stainless steel-selenium alloy cathode in accordance with this invention, are demonstrated.

Additive Selenium in Current deposited S01, B28003, efiiciency, manganese, Test number gm./l. grnJl. percent Cathode percent 1 0. 2 None 63 Stainless steel..- 0. None 0.1 l 85 do O. O. 2 None 84. 9 Stainless steel- I None selenium alloy.

I The lower limit of detectability is approximately 10 p.p.m.

EXAMPLE II The following tests demonstrate the effects obtained using several different stainless steel-selenium alloys in electrodepositing manganese metal in accordance with this invention.

Electrolyte and electrolysis conditions:

Temperature-35 C.

Current Se in Se, efficiency, deposited Alloy as cathode percent percent manganese 201 0. 75 None. 303 $0...- O. 29 85. 3 Do. 416 So 0.20 83 Do.

1 Lower limit of detectability is approximately 10 p.p.m.

As indicated above, use of each of the three different alloys resulted in the electrodeposition of manganese metal free of selenium contamination and in operations at high current efficiencies.

What is claimed is? 1. In the method of electrodepositing manganese metal from an electrolyte containing a source of manganese wherein the improvement comprises using as a cathode an alloy of stainless steel and selenium.

2. The method of claim 1 wherein the selenium is present in the alloy in an amount of from about 0.1 to 0.7%.

3. The method of claim 2 wherein the stainless steel is an austenitic stainless steel.

4. The method of claim 1 wherein the electrolyte comprises an aqueous solution containing from about to gm./liter of ammonium sulfate, from about 0.15 to 0.2 gm./ liter of sulfur dioxide and the source of manganese is manganous sulfate present in an amount of from about 14 to 35 gm./liter.

'5. The process of claim 4 wherein the alloy is an austenitic stainless steel containing from about 0.15 to 0.3 percent selenium.

References Cited Effect of Selenious Acid on the Electrodeposition of Mn, by Rao et al., Electrochem. Tech. Nov.-Dec. 1966, vol. 4, pp. 53 6-539.

TA-HSUNG TUNG, Primary Examiner R. L. ANDREWS, Assistant Examiner U.S. Cl. X.R. 4 204--293 

